Variational theory is a mathematical approach used to approximate the ground state (lowest energy state) of a quantum system. It involves finding the best possible approximation to the ground state by varying a trial wave function and minimizing the energy.
The ground state is the lowest energy state of a quantum system, while non-ground states are higher energy states. In variational theory, the goal is to find the best approximation to the ground state, as it is the most stable and physically meaningful state.
Variational theory works by using a trial wave function, which is a mathematical function that approximates the true wave function of a quantum system. The trial wave function is then varied and optimized in order to minimize the energy, resulting in an approximation of the ground state.
Variational theory allows for the calculation of approximate solutions to quantum systems that cannot be solved exactly. It also provides a way to estimate the ground state energy and other properties of a system, which can be useful in understanding and predicting the behavior of physical systems.
Yes, there are some limitations to variational theory. It can only provide an approximation to the ground state, and the accuracy of the approximation depends on the choice of trial wave function. Additionally, it may not be applicable to highly complex systems, and it does not provide any information about excited states.